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FORCES 5.2

FORCES 5.2. Chapter Five: Forces. 5.1 Forces 5.2 Friction 5.3 Forces and Equilibrium. Chapter 5.2 Learning Goals. Define friction. Identify causes of friction. Distinguish among various types of friction. Key Question: How does friction affect motion?. Investigation 5B. Friction.

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FORCES 5.2

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  1. FORCES 5.2

  2. Chapter Five: Forces • 5.1 Forces • 5.2 Friction • 5.3 Forces and Equilibrium

  3. Chapter 5.2 Learning Goals • Define friction. • Identify causes of friction. • Distinguish among various types of friction.

  4. Key Question: How does friction affect motion? Investigation 5B Friction

  5. 5.2 Friction • Frictionis a force that resists the motion of objects or surfaces. • Many kinds of friction exist.

  6. 5.2 Friction

  7. 5.2 Friction and two surfaces • Friction depends on both of the surfaces in contact. • When the hockey puck slides on ice, a thin layer of water between the rubber and the ice allows the puck to slide easily.

  8. 5.2 Identifying friction forces • Friction is a force, measured in newtons just like any other force. • Static friction keeps an object at rest from moving.

  9. 5.2 Identifying friction forces • Sliding friction is a force that resists the motion of an object moving across a surface.

  10. 5.2 A model for friction • Friction depends on a material’s properties such as roughness, how clean the surfaces are, and other factors. • The greater the force squeezing two surfaces together, the greater the friction force.

  11. 5.2 Reducing the force of friction • Unless a force is constantly applied, friction will slow all motion to a stop eventually. • It is impossible to completely get rid of friction, but it can be reduced.

  12. 5.2 Reducing the force of friction • The friction between a shaft (the long pole in the picture) and an outer part of a machine produces a lot of heat. • Friction can be reduced by placing ball bearings between the shaft and the outer part.

  13. 5.2 Using friction • Friction is also important to anyone driving a car. • Grooved tire treads allow space for water to be channeled away from the road-tire contact point, allowing for more friction in wet conditions.

  14. 5.2 Using friction • Shoes are designed to increase the friction between their soles and the ground. How do you think these shoes increase friction?

  15. 5.2 Friction and energy • Friction changes energy of motion into heat energy.

  16. 5.2 Friction and energy • Friction is always present in any machine with moving parts. • If the machine is small, or the forces are low, the amount of heat produced by friction may also be small.

  17. 5.2 Friction and energy • Each time two moving surfaces touch each other, tiny bits of material are broken off by friction. • Breaking off bits of material uses energy.

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